Patemo Biichi reaction

The mechanism of the Patemo-Biichi reaction is not well understood, and while a general pathway has been proposed and widely aceepted, it is apparent that it does not represent the full scope of reactions. Biichi originally proposed that the reaction occurred by light catalyzed stimulation of the carbonyl moiety 1 into an excited singlet state 4. Inter-system crossing then led to a triplet state diradical 5 which could be quenched by olefinic radical acceptors. Intermediate diradical 6 has been quenched or trapped by other radical acceptors and is generally felt to be on the reaction path of the large majority of Patemo-Biichi reactions. Diradical 6 then recombines to form product oxetane 3. 

It is evident from the exceptions noted that the mechanism proposed above does not fully capture the pathways open to the Patemo-Biichi reaction. A great deal of effort has been devoted to deconvoluting all of the possible variants of the reaction. Reactions via singlet state carbonyls, charge-transfer paths, pre-singlet exciplexes, and full electron transfer paths have all been proposed. Unfortunately, their influence on product 

The most valuable characteristic of the Patemo-Buchi reaction is the ability to set multiple stereocenters in one reaction and the development of diastereocontrolled reactions has been a major theme of research concerning this reaction. Stereocontrol can be envisioned to spring from either the carbonyl or the alkene and be controlled by either the substrate directly or by a chiral auxiliary. Little success has been achieved in substrate-induced selection by the carbonyl the most successful results were produced by 

Zamojski and Jarosz using cyclic ketone 23 with furan that generated a 75 25 ratio of diastereomers 24 and 25. 

Ironically, auxiliary-induced control via the alkene failed to generate synthetically useful selectivities, but direct substrate-induced control did. In particular, chiral silyl enol ethers with stereocenters in the y-position allowed the synthesis of enantiomerically 

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Patemo-Biichi reaction between 2-methylfuran 31 and an a-hydroxyaldehyde 30 to form the core oxetane. Two of the three stereocenters set in the electrocyclization appear in the final product while the third is selectively reversed with anomeric assistance. 

Given the relatively rare appearance of oxetanes in natural products, the more powerful functionality of the Patemo-Biichi reaction is the ability to set the relative stereochemistry of multiple centers by cracking or otherwise derivitizing the oxetane ring. Schreiber noted that Patemo—Btlchi reactions of furans with aldehydes followed by acidic hydrolysis generated product 37, tantamount to a threo selective Aldol reaction. This process is referred to as photochemical Aldolization . Schreiber uses this selectivity to establish the absolute stereochemistry of the fused tetrahydrofuran core 44 of the natural product asteltoxin. ... 

Patemo-Biichi reaction in preparation and transformations of 3-oxetanols and 3-aminooxetanes 97LA1627. 

The [2+2] photocycloaddition of an aldehyde or a ketone to an alkene to form an oxetane (e. g. Ill + IV —> V, Scheme 1) is a process that is known as the Patemo-Biichi reaction 8 it is a reaction that was first reported by Patemo in 19094 and was confirmed approximately forty-five years later by Biichi.Sa A particularly interesting variant of the Patemo-Biichi reaction is illustrated in... 

In the context of photoinduced [2 -I- 2] cycloadditions, the reaction of an olefin with a carbonyl center, known as the Patemo-Biichi reaction, has to be mentioned. The resulting oxetanes are thereby produced with high regioselectivity and stereoselectivity. 

Scheme 53 Mechanistic details of the Patemo-Biichi reaction.

In addition to the intermolecular Patemo-Biichi reaction, the intramolecular variant has also been studied the latter allows for the construction of bicyclic structures in one step. For example the diketone 8 reacts quantitatively to the bicyclic ketone 9 ... 

Although the Patemo-Biichi reaction is of high synthetic potential, its use in organic synthesis is still not far developed. In recent years some promising applications in the synthesis of natural products have been reported. The scarce application in synthesis may be due to the non-selective formation of isomeric products that can be difficult to separate—e.g. 6 and 7—as well as to the formation of products by competitive side-reactions such as Norrish type-I- and type-II fragmentations. 

Allylic strain is employed in the Patemo-Biichi reaction of a silyl enol ether and benzaldehyde.79 Using a bulky or polar substituent y to the ether as stereogenic locus, diastereomerically pure oxetanes with four contiguous chiral centres have been prepared. 

First reported in 1909, the photochemical [2+2] cyclization between alkenes and carbonyl compounds, known as the Patemo-Biichi reaction, is one of the most commonly used methods of synthesizing oxetanes. The scope of the reaction is however limited and only occurs readily between electron-rich alkenes and electron-poor carbonyls. The importance of the reaction is that, with careful selection of alkenes and carbonyl compounds, high regio- and stereoselectivities can be achieved (see CHEC(1984) and CHEC-II(1996) for previous examples) < 1984CHEC(7)363, 1996CHEC-II(1)721>. 

The Patemo-Biichi reaction is a milestone in organic photochemistry (Scheme 3.1). Paterno and Chieffi [1] reported obtaining oxetanes from the photocycloaddition of ketones to olefins in 1909, but this reaction was recognized as an important synthetic reaction only after the work of Biichi et al. [2]. 

The Patemo-Biichi reaction is a photocycloaddition reaction of a n,ji carbonyl compound to an alkene in the ground state from either the Si or the rl i state. The reaction can occur through the initial C O bond formation or through a previous formation of the C—C bond. A frontier orbitals approach can be used to explain the formation of oxetanes. We can observe the HSOMO-LUMO interaction in which the half-occupied ji carbonyl orbital interacts with the unoccupied ji molecular orbital of an electron-deficient alkene, and a C,0-biradical is formed. The LSOMO-HOMO interaction in which the half-occupied n orbital of the carbonyl O atom interacts with the ji orbital of an electron-rich alkene, and a C,C-biradical is formed [13, 14]. 

Figure 3.1. Biradical intermediate in the Patemo-Biichi reaction between furan and benzaldehyde.

In conclusion, the regiochemical behavior (the attack of the oxygen on an a-carbon or on a p-carbon of the furan ring) of the Patemo-Biichi reaction on furan, 2-methylfuran, and 2-furylmethanol can be explained considering the... 

The reported results represent all the available data on the Patemo-Biichi reaction on pentaatomic heterocycles that are not furan. There are very few data in particular, (1) most of the unsubstituted compounds tested did not react and (2) only a few substituted derivatives showed a significative reactivity toward excited carbonyl compounds. 

Another open question is related to the diastereoselectivity of the reaction. We have shown that Adam s rule cannot be used to explain the observed stereoselectivity in the reaction with 2-furylmethanol derivatives. If Adam s hypothesis does not work, the diastereoselectivity of the Patemo-Biichi reaction with allylic alcohols remains to be explained. 

The Generally Accepted Mechanism of the Patemo-Biichi Reaction... 

N Plath, M.W., and Runsink, J. (1989) Chiral Induction in photochemical reactions 10. The principle of isoinversion A model of stereoselection developed from the diastereoselectivity of the Patemo-Biichi reaction. Journal of the American Chemical Society, 111, 5367-5373. 

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